A giant arms hoard in Afghanistan thought to have been abandoned by al-Qaeda fighters has been destroyed by British Royal Marines.

In what is believed to be the biggest controlled explosion since World War II, specialist troops simultaneously blew up four caves full of ammunition.

There were an estimated 35,000 shells, rockets and mortars among the haul in the Paktia province.

It is thought the arms belonged to al-Qaeda and Taleban fighters who have fled the country, probably across the Pakistan border 60 kilometres (40 miles) away.

Soldiers toiled in the caves to set the explosives

The caves were found to be sealed by metal doors and one was estimated to hold 30 truckloads of arms.

Some of the weapons, made in Russia and China, were primed and ready to fire.

The marines used plastic explosives strapped to the weapons inside the caves.

Their task was to collapse the caves to cover the arms and prevent the caves being used again.

Booby traps

Commanders believed the caves to have been recently occupied and the arms disturbed.

Fears of booby traps meant the soldiers had to explore the caves with extreme caution.

Sergeant Stephen Woods of the Royal Marines said: "Obviously the local warlords or militia are going to protect their munitions so therefore we go on the principle that there is a booby trap there before we go into the cave itself. So therefore it is of high threat to us."

Once the charges were set the soldiers moved back a safe distance to trigger the blasts, which sent flames high into the air and produced a huge dust cloud.

A 50 metre (150 foot) crater was left behind.

The caves were sealed and abandoned

BBC correspondent Paul Welsh joined the marines on the operation and was taken to see one of the caves, 2,000 metres (7,000ft) above sea level, before they were destroyed.

He said the intensity of the explosions, which continued for 15 hours through the night, shocked even the demolition experts.

The destruction of the caves was part of the two-week old Operation Snipe, which is aimed at flushing out remaining Taleban and al-Qaeda fighters and destroying their infrastructure.

The 1,000-strong force is led by Royal Marines from 45 Commando, but it is yet to encounter combat.

Last week, commanders were forced to defend the success of the mission against accusations it was a "mockery".